Refactoring to ease cherry-pick

This change contains the parts of internal change
I916cf878469280e6c9498baf2cf930e140c3a386 that affect
GnssTimeUpdateService and its test. Pulling in these changes makes the
following cherry-pick easier to apply and follow. The rest of I916cf8
will follow naturally as part of the usual publishing of changes.

Bug: 236611620
Test: build / boot as part of the following cherry-pick
Change-Id: I111189d10836906c67a8fedeb2c9ecee6ab83026
Merged-In: I916cf878469280e6c9498baf2cf930e140c3a386